This invention relates to systems for transmitting data over packet-based networks.
It is known to send real-time or near-real-time information over packet-based networks, such as the internet. In internet telephony, for example, a sending system digitizes a talker""s speech and sends it over the internet in a sequence of packets to a receiving system. The receiving system then reassembles the speech and plays it back to a listener. Each of the packets transferred over the network during this process typically includes a header containing routing information followed by a data field containing the digitized speech data. To reduce noticeable lags, which are objectionable to most listeners, it can be beneficial to assemble short packets and immediately send them over the network, instead of waiting to accumulate a larger amount of data.
In one general aspect, the invention features a network communication system that includes a packet translator operatively connected between a tributary network port and a trunk network port. A tributary format is communicated through the tributary network ports and includes tributary packets that each include a header field and a data field. An aggregate format is communicated through the trunk network port, and includes a packet that includes an aggregate header field and the data fields.
The aggregate format can include a packet that includes an aggregate header field and a list with variable-length entries each including one of the data fields. The aggregate header field can include an aggregate packet format update field including an indication of a change in the aggregate packets and a reference to a position in the list. The aggregate packet format update field can include an indication of an addition of data from a tributary packet, a reference to a position in the list, and a destination derived from the tributary packet. The aggregate packet format update field can also include an indication of a deletion of data from a tributary packet in the aggregate packet and a reference to a position in the list. The tributary packets can each include a compressed header field compressed according to a single-destination header compression method. The system can include means responsive to an acknowledgment of receipt of a change tag to cause the packet translator to assemble aggregate packets with the same change tag until the system receives the acknowledgement. It can also include means for inserting a header checksum in each of the aggregate packets. It can further include means responsive to a fragmentation indication to reduce a size of the aggregate packets.
In another general aspect, the invention features a network communication method that includes assembling for each of a plurality of aggregate packets a list that includes a plurality of data fields and providing for each of the packets a header that includes destination information. The method also includes assembling for at least some of the aggregate packets a change tag indicating a position of a field in the list to be changed, and sending the aggregate packets that include the list, the header, and any change tag over a network from a source to a destination according to the destination information.
The method can further include the step of receiving tributary packets from different tributary nodes each including a header and a data field, the step of assembling a list can include assembling the data fields from the tributary packets to form the list of data fields, and the step of assembling a change tag can include destination information derived from one of the tributary packets in the change tag. The step of receiving tributary packets can receive tributary packets from a single-destination connection that employs header compression. The method can also include receiving an acknowledgement of receipt of a change tag, and the step of sending can send aggregate packets with the same change tag until then. The steps of assembling and sending can operate on data fields that include real-time digitized information. The steps of assembling and sending can operate on data fields that include digitized voice signals. The method can further include receiving a fragmentation indication after the step of sending, and reducing a size of the aggregate packets in response to the fragmentation indication. The step of assembling a list can assemble a list with variable-length entries. It can also assemble a list with some null entries.
The method can further include interpreting the change tags at the destination, and retrieving data from the fields from different ones of the packets assembled in the step of assembling at the destination based on the contents of the tags. The change tag can be an add tag that identifies a new field in the list, and the retrieving step can respond to the add tag by retrieving data from the new field. The change tag can also be a delete tag that identifies a deleted field in the list, and the retrieving step can respond to the delete tag by ceasing to retrieve data from the deleted field. The method can further include constructing tributary packets from the data fields retrieved in the step of retrieving using destination information obtained from the change tag. The packets constructed in the step of constructing can be sent over a connection that employs header compression.
In a further general aspect, the invention features a network communication method that includes the steps of receiving aggregate packets from a source, the packets each including a list that includes a plurality of data fields and a header, where at least some of the packets include a change tag indicating a position of a field in the list to be changed. The method also includes interpreting the change tags, and retrieving different data fields from different aggregate packets at the destination based on the contents of the change tags.
The method can also include constructing tributary packets from the data fields retrieved in the step of retrieving using destination information obtained from the change tag. The packets constructed in the step of constructing can be sent over a connection that employs header compression. The method can further include acknowledging receipt of a change tag. The method can further include verifying a header checksum in each of the aggregate packets. The steps of receiving and retrieving can operate on data fields that include real-time digitized information. The steps of receiving and retrieving can operate on data fields that include digitized voice signals. The method can further include detecting fragmentation of the aggregate packets and providing a fragmentation indication. One of the change tags can be an add tag that identifies a new field in the list, and the retrieving step can respond to the add tag by retrieving data from the new field. One of the change tags can also be a delete tag that identifies a deleted field in the list, and the retrieving step can respond to the delete tag by ceasing to retrieve data from the deleted field. The step of retrieving can retrieve variable-length entries from the list.
In another general aspect, the invention features a memory for storing data for access by a node on a network that includes an aggregate packet structure stored in the memory. The aggregate packet structure can include a list that includes separate data fields stored in the memory, a header stored in the memory that includes destination information for the first aggregate packet, and a change tag stored in the memory. The change tag includes a position indication stored in the memory and indicating a position of a field in the list to be changed.
The change tag can include one of an add tag and a subtract tag stored in the memory. The aggregate packet can further include a header checksum stored in the memory. The memory can further include a second aggregate packet structure stored in the memory. This second aggregate packet structure can include a second list that includes a plurality of separate data fields stored in the memory, a second header stored in the memory that includes destination information for the second aggregate packet, and a copy of the first change tag stored in the memory. The copy of the change tag can include a position indication stored in the memory and indicating a position of the field in the list to be changed.
Systems according to the invention may permit significant bandwidth reductions in network communication, including near-real-time or real-time network communication. Because header information is stripped from shorter packets, and data from these packets are placed in aggregate packets that carry a proportionally smaller amount of header information, the overall burden of the network is reduced. This can result in reduced average network latency or in an increase in the number of packets that can be sent over a network. Systems according to the invention can also reduce header overhead while maintaining low network latency. Such systems can exhibit better overall efficiency than systems that send a number of individual packets in a single session, and can exhibit better latency specifications than systems that block short packets into larger ones.
Operation of systems according to the invention can be made transparent to end-users of the network. The bandwidth savings available from such systems can therefore be immediately available to individual users of a network even if they are only temporarily connected. And these end users do not need to upgrade or modify their systems in any way.
Systems according to certain aspects of the invention can also be beneficial in that they can robustly handle varying levels of traffic. By employing aggregate packets with variable-length lists of variable-length entries, such systems can efficiently handle a variable number of tributary packets and sequences of packets of varying lengths. This can permit these systems to operate in networks with different statistical characteristics, networks with dynamically changing traffic patterns, and/or in networks to which varying types of tributaries are attached at any given moment.
Systems according to the invention may also have an impact on the statistical characteristics of network performance. This is particularly beneficial in environments where a network is optimized to manage larger packets than those typically sent over the network, because smaller packets are consolidated into larger ones. Conversely, this facet of the invention can allow a designer to optimize his or her network configuration for larger packets, which tends to improve network efficiency.